Joachim Durchholz wrote: > Marshall schrieb: > > Now, I'm not fully up to speed on DBC. The contract specifications, > > these are specified statically, but checked dynamically, is that > > right? > > That's how it's done in Eiffel, yes. > > > In other words, we can consider contracts in light of > > inheritance, but the actual verification and checking happens > > at runtime, yes? > > Sure. Though, while DbC gives rules for inheritance (actually subtypes), > these are irrelevant to the current discussion; DbC-minus-subtyping can > still be usefully applied.
Yes, subtyping. Of course I meant to say subtyping.<blush> I can certainly see how DbC would be useful without subtyping. But would there still be a reason to separate preconditions from postconditions? I've never been clear on the point of differentiating them (beyond the fact that one's covariant and the other is contravariant.) > > Wouldn't it be possible to do them at compile time? (Although > > this raises decidability issues.) > > Exactly, and that's why you'd either uses a restricted assertion > language (and essentially get something that's somewhere between a type > system and traditional assertion); or you'd use some inference system > and try to help it along (not a simple thing either - the components of > such a system exist, but I'm not aware of any system that was designed > for the average programmer). As to the average programmer, I heard this recently on comp.databases.theory: "Don't blame me for the fact that competent programming, as I view it as an intellectual possibility, will be too difficult for "the average programmer" -you must not fall into the trap of rejecting a surgical technique because it is beyond the capabilities of the barber in his shop around the corner." -- EWD512 > > Mightn't it also be possible to > > leave it up to the programmer whether a given contract > > was compile-time or runtime? > > I'd agree with that, but I'm not sure how well that would hold up in > practice. I want to try it and see what it's like. Marshall -- http://mail.python.org/mailman/listinfo/python-list
